Unlike conventional salt or dye tracers, artificial/synthetic DNA hydrologic tracers are essentially non-toxic and several can be used simultaneously. These features have implications for DNA to be used to better understand environmental processes and map hydrological pathways in complex environments, such as watersheds. Synthetic DNA tracers also have the potential to help with a better understanding of the behaviour of environmental DNA (eDNA) and its application in biomonitoring. Some components of eDNA exist as free/naked DNA not bound to other substances or protected by cellular material. The goal of the current research was to assess the fate and transport of naked DNA (short single stranded DNA sequences) in a small stream as a potential environmental tracer. As a proof-of-concept, two unique DNA tracers were released into an upstream location in Washington Creek (southern Ontario). After releasing the tracers, water samples were collected 100 m and 350 m downstream and breakthrough curves of tracer concentration were plotted over time. Both tracers behaved similarly with a mass recovery of 71% (T11) and 80% (T22) at the 100 m downstream sampling location and about 70% for both tracers at 350 m downstream. The downstream tracer peak arrival times were 15 – 16 min and 30 – 31 min at the 100 m and 350 m sampling sites, respectively, demonstrating that naked DNA injected into the stream can quickly travel downstream. This suggests that eDNA, in the naked form, may survive considerable distances downstream from the source and has implications for biomonitoring strategies. Additional unique DNA tracers were designed and optimized for future experiments. DNA tracers create many opportunities for applications in environmental sciences, especially if they can be combined with other substances to alter their environmental properties and fate (i.e., nanoparticles). DNA tracers can be attached to nanoparticles to protect DNA degradation in harsh environments or influence their zeta potential.

High-latitude cold regions are warming more than twice as fast as the rest of the planet, with the greatest warming occurring during the winter. Warmer winters are associated with shorter periods of snow cover, resulting in more frequent and extensive soil freezing and thawing. Freeze-thaw cycles (FTC) influence soil chemical, biological, and physical properties and any changes to winter soil processes may impact carbon and nutrients export from affected soils, possibly altering soil health and nearby water quality. Changes to non-growing season climate affect soil biogeochemical processes and fluxes and understanding these changes is critical for predicting nutrient availability in cold region ecosystems and their impacts on downstream water quality. These impacts are relevant for agricultural soils and practices in cold regions as they are important in governing water flows and quality within agroecosystems. Agricultural systems are source areas for nutrient pollutants due to fertilizer use and have been the target of numerous management strategies. Sustainable agricultural practices have been increasingly employed to mitigate nutrient loss due to erosion, but nutrient export via surface runoff, subsurface leaching, and volatilization allows for continued high nutrient losses (Beach et al., 2018; King et al., 2017). Chapter 1 of thesis discusses the non-growing season climate changes altering winter soil processes and reviews the major nitrogen transformation processes leading to nitrogen losses in agricultural soils. In Chapter 2, I present a soil column experiment to assess the leaching of nutrients from fertilized agricultural soil during the non-growing season. Four soil columns were exposed to a non-growing season temperature and precipitation model and fertilizer amendments were made to two of the columns to determine the efficacy of fall-applied fertilizers and compared to other two unfertilized control columns. Leachates from the soil columns were collected and analyzed for cations and anions. The experiment results showed that a transition from a freeze period to a thaw period resulted in significant loss of chloride (Cl-), sulfate (SO42-) and nitrate (NO3-). Even with low NO3- concentrations in the applied artificial rainwater and fertilizer, high NO3- concentrations (~150 mg L-1) were observed in fertilized column leachates. Simple plug flow reactor model results indicate the high NO3- leachates are found to be due to active nitrification occurring in the upper oxidized portion of the soil columns mimicking overwinter NO3- losses via nitrification in agricultural fields. The low NO3- leachates in unfertilized columns suggest that FTC had little effect on N mineralization in soil. In Chapter 3, I provide a brief review of nitrification inhibitors and how soil properties impact nitrification inhibitor efficacy. There are only a few studies on the relationship between nitrification inhibitor efficacy and climatic factors, especially in regard to FTC. I conducted a sacrificial soil batch experiment to determine if and how nitrification inhibitors were impacted by FTC to further explore the results of Chapter 2. The batch experiment revealed the nitrification inhibitors were effective at mitigating NO3- production under freeze-thaw conditions but more effective at mitigating these losses under thaw conditions. The soils exposed to the FTC condition experienced significant N mineralization flushes in contrast to the lack of mineralization induced by FTCs in the experiment detailed in Chapter 2. In Chapter 4, I summarize the key findings of this thesis. The results showed fertilizer loss and nitrification inhibitor effectiveness are affected by freeze-thaw cycling in arable soil. The experimental and modeling results reported in this thesis could be used to bolster winter soil biogeochemical models by elucidating nutrient fluxes over changing winter conditions to refine best management practices for fertilizer application. Ultimately, these results and the conclusions drawn from them highlight several research pathways that could be undertaken to progress our understanding of the complex interactions between FTC and fertilizer dynamics.

With recent developments in oil and gas exploration technologies that have opened regions of Canada’s northern territories and the threat of climate change, uncertainties around how these factors may impact the environment in these areas are profuse. To reduce uncertainty and allow for mitigation planning, having effective baseline monitoring of environmental systems, such as groundwater, is critical. However, baseline monitoring studies of groundwater resources in these regions are complex and expensive to undertake as compared to studies in more southern regions. This is due mainly to the remoteness, lack of infrastructure and presence of discontinuous permafrost that complicates the use of traditional groundwater monitoring methods in northern regions. The work outlined in this thesis set out to improve baseline monitoring studies of groundwater in discontinuous permafrost areas. A suite of geochemical and isotopic tracers combined with physically based hydrologic measurements were tested in two summer field campaigns within the Bogg Creek Watershed, a small subcatchment of the Mackenzie River in the Northwest Territories (NWT). These data were acquired through strategic sampling utilizing portable and lightweight equipment, guided by previous remote sensing work and an aerial infrared survey. This field data was combined with a variety of other data sets acquired through public records and reports, as well as through collaboration with interested third parties. Physical data provided evidence for groundwater discharge in some areas, while the geochemical and isotopic evidence allowed for fingerprinting of these groundwater sources. In total, 5 groundwater source groups were identified in the study area. These included shallow seepage water and organic active layer porewater (both Ca-SO4¬), suprapermafrost groundwater originating from mineral soils (Ca-HCO3), subpermafrost groundwater from the Little Bear Formation aquifer (Na-HCO3), and subpermafrost groundwater from the Martin House Formation (Na-Cl/HCO3). Evidence of suprapermafrost and subpermafrost groundwater contributions were found in Bogg Creek and its headwater tributaries as well as in several springs. Suprapermafrost groundwater influence occurs throughout the watershed but is most dominant in upland tributaries. Evidence for Little Bear Formation groundwater influence was found in the geochemical and 87Sr/86Sr signature of one of the tributaries of Bogg Creek, downstream of several mapped icings. Evidence of Martin House Formation groundwater influence was noted in geochemistry from a spring complex, associated with mapped icings. This spring water appeared to be mixtures of both subpermafrost and suprapermafrost groundwaters, but this is not certain. There is also evidence for Martin House Formation water in the lower reaches of Bogg Creek. δ18O and δ2H data suggest these contributions are quite small within the creek and its tributaries but are more substantial in springs. This highlights the sensitivity inherent in each method, where geochemistry is quite responsive to minor contributions of subpermafrost groundwater due to a much higher degree of contrast between solute concentrations in suprapermafrost and subpermafrost groundwater endmembers. There is less contrast in δ18O and δ2H. 87Sr/86Sr appeared to confirm what was indicated in the geochemical results, while δ13C in CH4 and 3H were inconclusive. A conceptual model of the site hydrogeologic system was developed based on this information. Some uncertainty remains on exact groundwater origins due to the limitations of the geochemical and isotopic species used, but overall results indicate that these techniques could be applied in similar discontinuous permafrost environments. Portable sampling techniques used in the shallow subsurface might be able to effectively characterize suprapermafrost groundwaters in an area quickly and efficiently, limiting the need for extensive monitoring well networks. Large contrasts from this water found in surface water or springs may be indicative of water originating from another source, such as from a subpermafrost aquifer. However, a certain amount of subpermafrost groundwater sampling is needed, as many uncertainties arise with missing endmembers.